This invention relates to methods, apparatus and solutions for relieving arterial constrictions caused by deposition of plaque in arteries, particularly coronary arteries.
Recently an alternative approach to coronary bypass surgery has been developed. In this non-operative procedure for the improvement of blood flow in patients with coronary artery disease, a catheter with an inflatable balloon at the distal end is inserted into the femoral artery or by brachial cutdown, and is positioned by fluoroscopic control at the appropriate coronary ostium. The process is known as percutaneous transluminal coronary angioplasty (PTCA).
The balloon at the distal end of the catheter has a predetermined maximum diameter. It is filled with a radio opaque dye to permit visualization. Alternatively, the balloon itself may be radio opaque. When the balloon is positioned in the stenosis it is inflated for from 3 to 5 seconds and then deflated. The inflation cycle may be repeated several times to achieve satisfactory results. Normally the luminal diameter of the stenotic vessel increases at least 20% as a result of the treatment.
The procedure has been employed for treatment of single, large atherosclerotic lesions of the coronary, renal, iliac and even vertebral arteries. The effect of the expanded balloon is to literally blow open the stenotic zone. Disruption of the wall is marked, including fracture of the calcium in the lesion, tearing of the plaque itself and extravasation of plaque lipid and gruel into the adjacent vessel wall. Complications include hemorrhage, tears of the wall and sudden blockage of the damaged area with a clot. It is standard procedure to conduct the treatment with a standby surgical team. Emergency surgery is required from time to time.
The procedure is, in effect, a vigorous attack on a delicate system. However, with well selected patients in the hands of an experienced balloon team, the success rate is close to 90%. There is room for improvement. A system which would permit a less forceful attack on the plaque and on the arterial walls would generate fewer complications, increase the number of patients who could be successfully treated, and be generally more acceptable.
PTCA does not generally dissolve the plaque. It merely compresses it and forces it into the arterial wall. The total mass of the plaque is not appreciably reduced. It is, however, possible that the alteration of the atheroma structure, perhaps by redistribution of its elements, permits the eventual dissolution of at least some of the plaque. It appears that the remaining plaque body resulting from PTCA may serve as the nucleus for the formation of new plaque since restenosis has been observed in some patients.
Atherosclerotic plaques vary considerably in their composition from site to site, but certain features are common to all of them. They contain many cells, mostly these are derived from cells of the wall that have divided wildly and have grown into the surface layer of the blood vessel, creating a mass lesion. Plaques also contain cholesterol and cholesterol esters, commonly referred to as fat. This lies freely in the space between the cells and in the cells themselves. A large amount of collagen is present in the plaques, particularly advanced plaques of the type which cause clinical problems. Additionally, human plaques contain calcium to varying degrees, hemorrhagic material including clot and grumous material composed of dead cells, fat and other debris. Relatively large amounts of water are present as is typical of all tissue.
In accordance with the methods of this invention arterial constrictions are relieved, not by forcing them into the arterial wall, or by fracturing or tearing, but by dissolving at least a portion of the plaque.